Conventionally, known is a finger vein authentication device which registers in advance the vein pattern of a person's finger as biological information, and authenticates or identifies an individual based on the process of matching the foregoing registered biological information and the vein pattern of the presented finger. In PTL 1, a finger vein authentication device includes a light source which irradiates a person's finger with near-infrared light, an imaging unit which captures an image of a vein pattern, and an information processing unit which matches the photographed vein pattern and a pre-stored registered finger vein pattern and determines whether they are a match. In this kind of conventional finger vein authentication device, an optical reduction system is used as the optical system of the imaging unit.